Methods for fabricating a helicopter main rotor blade

ABSTRACT

A method for fabricating a helicopter main rotor blade includes a compaction fixture for assembling and compacting blade subassembly components and a sheath spreading/insertion apparatus for spreading and inserting a leading-edge sheath onto  in combination with the blade subassembly during the compaction process. The compaction fixture includes a lower assembly having a contoured upper airfoil nest mounted in combination with a support structure and an upper assembly having a pressure bag affixed in sealed combination to a contoured backplate affixed in combination to a structural support truss. The contoured upper airfoil nest includes a plurality of tooling pins for locating an upper composite skin in aligned combination on the contoured upper airfoil nest and a plurality of pusher pins for chordwise alignment of a spar assembly in the contoured upper airfoil nest. Spar stanchions affixed to the support structure provide spanwise alignment of the spar assembly in the contoured upper airfoil nest. With the upper and lower assemblies in locked combination, the pressure bag is pressurized to compact the assembled blade subassembly components.

RELATED APPLICATION

The instant application is related to commonly-owned, U.S. patentapplication is a divisional application U.S. patent application Ser. No.08/275,556, filed 15 Jul. 1994, now U.S. Pat. No. 5,430,937 and entitledAN EOP SCRIBE DEVICE (S-4887).

TECHNICAL FIELD

The present invention is directed to manufacturing apparatus andmethods, and more specifically, to apparatus and methods for fabricatinga helicopter main rotor blade.

BACKGROUND OF THE INVENTION

There is a growing trend in the aerospace industry to expand the use ofcomposite materials for a diverse array of structural and dynamicapplications. One particular application for the use of compositematerials lies in the fabrication of main rotor blades for helicopters.

With increased usage of composite materials to fabricate main rotorblades, the helicopter industry is continually seeking to improve thetooling and/or methods used to fabricate main rotor blades so as toreduce the per unit fabrication costs associated with the main rotorblades. Typically, the per blade fabrication costs are higher than needbe due to part rejections or rework that occurs during the main rotorblade fabrication process. Part rejections typically occur where thecomposite material has been so substantially damaged during thefabrication process that rework is not cost effective or where afinished fabricated part exceeds the tolerance limits established forthe part. Rework occurs where the composite material has been damagedduring the fabrication process, and the damage may be repaired in arelatively cost effective manner.

Sikorsky Aircraft has developed a parallel manufacturing protocol forfabricating helicopter main rotor blades wherein a blade subassembly anda leading-edge sheath are concurrently fabricated as individualcomponents, and then the prefabricated blade subassembly and theprefabricated leading-edge sheath are integrated in combination to forman assembled main rotor blade. The assembled main rotor blade issubsequently cured to form a finished main rotor blade. This protocolwas adopted in large measure because experience has shown that theleading edges of main rotor blades are subjected to varying degrees ofabrasion during helicopter operations. As a result of such abrasioneffects, the leading edge of a helicopter main rotor blade at some pointbecomes aerodynamically unsuitable for further use. Rather thanreplacing the entire main rotor blade, it was determined that areplaceable leading-edge sheath would allow abrasion-degraded main rotorblades to be efficaciously and economically repaired.

The prior art process for fabricating blade subassemblies involved theuse of a “clamshell” tooling fixture and a “wet” lay-up process for thecomposite materials. It was determined that the rejection rate for bladesubassemblies fabricated using the clamshell tooling fixture and the wetlay-up process was unacceptable in light of the today's competitivemarket. The dependability and accuracy of the clamshell tooling fixturedepended upon the stability of the laid up tooling contours, the propersecuring and pinning of all fasteners and locators, and the variabilityin applying blade outer mold line pressures. The clamshell toolingfixture and the wet lay-up process were subjected to shrinkage and loseof tolerances, which led to component rejection. The clamshellconfiguration result in asymmetrical pressure distributions across thelayed-up blade subassembly.

Another area of concern in the parallel manufacturing protocol was thesheath spreader tool used to integrate the leading-edge sheath incombination with the blade subassembly. The leading-edge sheath has aprefabricated configuration that does not allow the sheath to beinserted directly onto the blade subassembly. Rather, the aft edges ofthe leading-edge sheath must be spread apart to allow the leading-edgesheath to be inserted onto the blade subassembly. The prior art sheathspreader tool comprises segmented angular stainless steel sheet metalgrabbers that are mounted spanwise on the aft edges of the leading-edgesheath in contact with the inner mold line (IML) surfaces (which areformed of composite material) of the leading-edge sheath. Each segmentof the prior art grabber is individually actuated by means of a side camlever. The prior grabbers exert a shearing action against the IMLsurfaces of the leading-edge sheath in spreading the aft edges of thesheath apart. The shearing action caused by the prior art grabberscaused cracks and delaminations in the composite material subjected tothe shearing action thereof, resulting in component rejections orrework. In addition to the foregoing deficiency of the prior artleading-edge sheath spreader tool, the segments of the grabber areindividually actuated in a sequential manner such that to spread apartthe entire leading-edge sheath involves multiple, repetitive operations.Not only is such a procedure labor intensive and time consuming, andhence costly, such a procedure may induce unwanted stresses into the aftedges of the leading-edge sheath.

A need exists to provide an apparatus for spreading a leading-edgesheath for insertion onto a blade subassembly without inducing cracksand/or delaminations in the composite material of the leading-edgesheath. Preferably, the apparatus should spread the leading-edge sheathapart in a single operation to reduce the time required to spread theleading-edge sheath apart. A need also exists to provide a fixture forassemblage and compacting of a blade subassembly that provides a uniformpressure distribution during the compaction of the blade subassembly,that facilitates the use of prepreg composite materials, and thatensures proper chordwise and spanwise alignment of the components of theblade subassembly layed-up in the fixture. A need also exists to providea sheath spreading apparatus and compaction fixture which in combinationsimplify the insertion of a spread-apart leading-edge sheath onto theblade subassembly.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a sheathspreading/insertion apparatus that spreads apart a leading-edge sheathwithout inducing cracks and/or delaminations in the composite materialthereof.

Another object of the present invention is to provide a sheathspreading/insertion apparatus that spreads apart a leading-edge sheathin a single operation.

A further object of the present invention is to provide a compactionfixture for assemblage and compaction of blade subassembly componentsthat provides a uniform pressure distribution during compaction of theblade subassembly.

Still another object of the present invention is to provide a compactionfixture that ensures proper chordwise and spanwise alignment of thecomponents comprising the blade subassembly as assembled in thecompaction fixture.

One more object of the present invention is to provide a sheathspreading/insertion positioning apparatus and a compaction fixturewhich, in combination, greatly simplify the insertion of a spread-apartleading-edge sheath assembly onto in relation to the blade subassembly.

These and other objects of the present invention are achieved by asheath spreading/insertion positioning apparatus according to presentinvention for spreading a leading-edge sheath and inserting positioningthe spread-apart leading-edge sheath in combination with relation to ablade subassembly. The sheath spreading/insertion positioning apparatuscomprises a movable stanchion, an upper a first elongate carriage membermounted in movable combination with the movable stanchion and a lowersecond elongate carriage member mounted in movable combination with themovable stanchion. A plurality of suction cups are mounted incombination with each of the upper first and lower second elongatecarriage members. A means is provided by imparting synchronized movementto the upper first and lower second carriage members between adisengaged position wherein the leading-edge sheath may be insertedbetween the pluralities of suction cups mounted in combination with theupper first and lower second carriages without contact therewith, anengaged position wherein the pluralities of suction cups abuttinglyengage respective outer mold line (OML) surfaces of the leading-edgesheath, and an operating position wherein the leading-edge sheath isspread apart for insertion onto positioning in relation to the bladesubassembly. A means is provided for generating suction forces in thepluralities of suction cups in the engaged position to cause the suctioncups to hold the respective OML surfaces of the leading-edge sheath suchthat subsequent synchronized movement of the upper first and lowersecond carriage members to the operating position causes theleading-edge sheath to be spread apart. A means is provided for movingthe movable stanchion imparting relative movement between thespread-apart leading-edge sheath and the blade subassembly to insertposition the spread-apart leading-edge sheath onto in relation to theblade subassembly.

The sheath spreading/insertion positioning apparatus further includes ameans for indicating that the spread-apart leading-edge sheath has beenfully inserted onto positioned in relation to the blade subassembly. Thesynchronized movement imparting means comprises a plurality of pneumaticcylinders mounted in combination with the upper first elongate carriagemember and the movable stanchion, a plurality of pneumatic cylindersmounted in combination with the lower second elongate carriage membersand the movable stanchion, and a pressure source pneumaticallyinterconnected to the pluralities of pneumatic cylinders. Actuation ofthe pressure source provides pressurized air to the pluralities ofpneumatic cylinders to cause synchronized movement of the upper firstand lower second elongate carriage members between the disengagedposition wherein the leading-edge sheath may be inserted between thepluralities of suction cups mounted in combination with the upper firstand lower second elongate carriage members without contact therewith,the engaged position wherein the pluralities of suction cups abuttinglyengage respective OML surfaces of the leading-edge sheath, and theoperating position wherein the leading-edge sheath is spread apart forinsertion onto positioning in relation to the blade subassembly. For thedescribed embodiment, ninety suction cups are mounted in combinationwith the upper first elongate carrier member and ninety suction cups aremounted in combination with the lower second elongate carrier member.

To spread and insert position the leading-edge sheath in combinationwith relation to a blade subassembly, the leading-edge sheath is mountedbetween upper first and lower second rows of suction cups, the upperfirst and lower second rows of suction cups are displaced insynchronized movement to an engaged position wherein the suction cupsabuttingly engage respective OML surfaces of the leading-edge sheath,suction forces are generated in the upper first and lower second rows ofsuction cups to cause the suction cups to hold the respective OMLsurfaces of the leading-edge sheath, the upper first and lower secondrows of suction cups are displaced in synchronized movement to anoperating position to cause the leading-edge sheath to be spread apart,and the spread-apart leading-edge sheath is inserted onto positioned inrelation to the blade subassembly.

A compaction fixture according to the present invention is provided forassembling and compacting a blade subassembly that includes upper andlower composite skins, a honeycomb core, and a spar assembly (a sparwith at least one counterweight bonded thereto). The compaction fixturecomprises a lower assembly that includes a support structure and acontoured upper airfoil nest mounted in combination with the supportstructure. The contoured upper airfoil nest has an OML surface thatdefines the airfoil surface of the upper composite skin, a plurality oftooling pins for locating the upper composite skin, honeycomb corecombination in the contoured upper airfoil nest, and a plurality ofpusher pins for locating the spar assembly in chordwise alignment in thecontoured upper airfoil nest. A spar stanchion is mounted in combinationwith the inboard and outboard ends of the contoured upper airfoil nest,respectively, for locating the spar assembly in spanwise alignment inthe contoured upper airfoil nest. The compaction fixture furthercomprises an upper assembly that includes a structural support truss, acontoured backplate affixed to the structural support truss, and apressure bag having chordwise and spanwise dimensions corresponding tothe blade subassembly fastened in sealed combination with the contouredbackplate. A means is provided for locking the upper and lowerassemblies in combination so that compaction of the blade subassemblyassembled in the lower assembly may be effectuated. A means is providedfor pressurizing the pressure bag to compact the blade subassemblydisposed in the locked upper and lower assemblies. The compactionfixture may further include a caul plate interposed between the upperand lower assemblies to provide uniform pressure distribution over thelayed-up blade subassembly during compaction thereof.

To assemble and compact the blade subassembly, a composite fixture asdescribed in the preceding paragraph is provided. The upper compositeskin and the honeycomb core are layed-up in combination in the contouredupper airfoil nest. The spar assembly is located in chordwise andspanwise alignment in the contoured upper airfoil nest, and the lowercomposite skill is layed-up in combination with the spar assembly andthe honeycomb core. The upper and lower assemblies are locked incombination and the pressure bag is pressurized to compact the assembledblade subassembly.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention and the attendantfeatures and advantages thereof may be had by reference to the followingdetailed description when considered in conjunction with the followingdrawings wherein:

FIG. 1A is a top plan view of an exemplary main rotor blade for an H-60helicopter.

FIG. 1B is a cross-sectional view of the main rotor blade of FIG. 1Ataken along line 1B—1B thereof.

FIG. 1C is an enlarged partial perspective view of the leading edgesheath illustrated in FIG. 1B.

FIG. 1D is an enlarged partial perspective view of a counterweight forthe exemplary main rotor blade of FIG. 1A.

FIG. 2 is a perspective view of a compaction fixture and a sheathspreading/insertion apparatus according to the present invention.

FIG. 3 is a partial plan elevation view of the apparatus of FIG. 2.

FIG. 3A is a partial perspective view of the sheath spreading/insertionapparatus of FIG. 3.

FIG. 4A is a flow chart illustrating the assemblage and compactionprocess according to the present invention.

FIG. 4B is a flow chart illustrating the sheath spreading and sheathinsertion process according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The apparatus and methods described in further detail hereinbelowcomprise part of the manufacturing protocol for fabricating main rotorblades for H-60 helicopters manufactured by the Sikorsky AircraftDivision of United Technologies Corporation. In particular, theapparatus and methods described herein have particular utility forfabricating the H-60 growth main rotor blade developed by SikorskyAircraft. It will be appreciated, however, that the apparatus andmethods described herein have applicability in fabricating main rotorblades in general.

An H-60 growth main rotor blade 100 is exemplarily illustrated in FIGS.1A-1D, and includes a leading edge 102 and a trailing edge 104, which incombination define the chord of the rotor blade 100, and an inboard end106 and an outboard (tip) end 108 (an anhedral tip portion of the mainrotor blade 100, which is the portion of the blade outboard of thedashed line 109 in FIG. 1A, is separately fabricated as a replaceablecomponent for the main rotor blade 100), which in combination define thespan of the rotor blade 100. The main rotor blade 100 comprises upperand lower composite skins 110, 112 that define the upper and loweraerodynamic surfaces of the blade 100, respectively, a honeycomb core114, a spar 116, one or more counterweights 118, and a leading-edgesheath 120. Adjustable trim tabs 130 (two for the illustratedembodiment) extend rearwardly from the trailing edge 104. The upper andlower composite skins 110, 112, the honeycomb core 114, the spar 116,and the counterweights 118 in combination define a blade subassembly132.

The composite skins 110, 112 are prefabricated components formed fromseveral plies of prepreg composite material of a type know to thoseskilled in the art, e.g., for the described embodiment woven fiberglassmaterial embedded in a suitable resin matrix. The upper composite skin110 has a plurality of locator apertures 134 (see FIG. 1A) formedtherethrough to facilitate the location of the spar assembly 116/118 ina compaction fixture as described in further detail hereinbelow. Afterthe main rotor blade 100 has been assembled, the locator apertures 134are patched with composite material so that the upper composite skin 110has an aerodynamically smooth surface. The honeycomb core 114 isfabricated of material type typically used in aerospace applications,e.g., for the described embodiment NOMEX® (NOMEX is a registeredtrademark of E. I. du Pont de Nemours & Co., Wilmington, Del. for aramidfibers or fabrics) and functions as a low weight, structural stiffeningmember between the upper and lower composite skins 110, 112.

The spar 116 is a prefabricated component and functions as the primarystructural member of the main rotor blade 100, reacting the torsional,bending, shear, and centrifugal dynamic loads developed in the rotorblade 100 during operation of the helicopter. The spar 116 of thedescribed embodiment is a composite spar of the type disclosed andclaimed in commonly-owned, co-pending U.S. patent application Ser. No.07/995,219 filed 22 Dec. 1992 entitled FIBER REINFORCED COMPOSITE SPARFOR A ROTARY WING AIRCRAFT. The composite spar 116 comprises upper andlower side walls corresponding to upper and lower airfoil surfaces,respectively, and forward and aft conic closures corresponding toleading and trailing edges, respectively, of the main rotor blade 100.The upper and lower side walls comprise a plurality of pre-ply layers,each pre-ply layer including unipack plies and cross plies of prepregcomposite material, i.e., fibrous material embedded in a resin matrix.The unipack plies, which have longitudinally (axial) orientated fibers,are of equal width and staggered to provide a tapered edge with theupper and lower side walls. The cross plies, which have ±40° orientatedfibers, have varying widths that form a staggered butt joint about theperiphery of the forward and aft conic closures. While the describedembodiment of the main rotor blade 100 incorporates a composite spar116, one skilled in the art will appreciate that the apparatus andmethods of the present invention may also be utilized in manufacturingmain rotor blades wherein the spar is fabricated as a metallicstructural member, e.g., a titanium spar.

One or more counterweights 118, one of which is illustrated in furtherdetail in FIG. 1D, are utilized to statically and dynamically balancethe main rotor blade 100. The counterweights 118 are fabricated fromless dense to more dense materials, e.g., foam, tungsten, and lead,respectively, for the described embodiment, in the spanwise directionfrom the inboard end 106 to the outboard end 108 to provide thenecessary weight distribution for statically and dynamically balancingthe main rotor blade 100. The counterweights 118 are fabricated toinclude hardpoints 136 that provide the physical engagement between thecounterweights 118 and the inner mold line (IML) surface of the leadingedge sheath 120. The counterweights 118 are adhesively bonded to thespar 116 to form a spar assembly 116/118 wherein the bondedcounterweights 118 are in an interposed position between the leadingedge sheath 120 and the leading edge of the spar 116.

The leading edge sheath 120, which is illustrated in greater detail inFIG. 1C, is a prefabricated hybrid component fabricated from compositematerials and abrasion-resistive materials. The sheath 120 has agenerally V-shaped configuration that defines the leading edge 102 ofthe main rotor blade 100. The sheath 120 comprises one or more plies 122of prepreg composite material, e.g., woven fiberglass material embeddedin a suitable resin matrix for the described embodiment, that define theinner mold line (IML) of the leading edge sheath 120, a first abrasionstrip 124, and a second abrasion strip 126. For the described embodimentof the leading edge sheath 120, the first abrasion strip 124 isfabricated from titanium and the second abrasion strip 126 is fabricatedfrom nickel. The tip end 108, i.e., outboard end, of the leading edgesheath 120 has the nickel strip 126 bonded to the titanium strip 124 asillustrated in FIG. 1C. The titanium strip 124 with the nickel strip 126overlay is adhesively bonded to the prepreg composite plies 122 to formthe leading edge sheath 120. Exposed segments 128 of the prepregcomposite plies 122 facilitate adhesive bonding of the leading edgesheath 120 in combination with the blade subassembly 132. The exposedsegments 128 include finished edges 128A (a method and apparatus fordefining the finished edges 128A of the leading-edge sheath 120 isdescribed in commonly-owned, co-pending U.S. patent application entitledAN EOP SCRIBE DEVICE (S-4887)) that have been formed to define theproper integration of the leading-edge sheath 120 in combination withblade subassembly 132 The leading edge sheath 120 is removable tofacilitate replacement thereof. The leading edge sheath 120, and inparticular the titanium strip 124 and the nickel strip 126 overlay,provides abrasion protection for the leading edge 102 of the main rotorblade 100. The leading edge sheath 120 also provides control of airfoiltolerances of the main rotor blade 100.

With reference to FIGS. 2-3, 3A, the apparatus according to the presentinvention include a compaction fixture 10 and a sheathspreading/insertion apparatus 50. The compaction fixture 10 includes alower assembly 12 and an upper assembly 30, which, in securedcombination, define the compaction fixture 10 which is operative tocompact the assembled blade subassembly 132. The lower assembly 12comprises a contoured upper airfoil nest 14 mounted on a supportstructure 16. The contoured upper airfoil nest 14 has an outer mold line(OML) surface 18 that defines the OML of the upper airfoil surface ofthe rotor blade 100, i.e., the upper composite skin 110.

Affixed in combination with the OML surface 18 of the contoured upperairfoil nest 14 are a plurality of tooling pins 20 (five for thedescribed embodiment). The tooling pins 20 function as location markersfor locating the upper composite skin 110 in aligned combination on thecontoured upper airfoil nest 14. Also affixed in combination with theOML surface 18 of the contoured upper airfoil nest 14 are a plurality ofpusher pins 22 (three for the described embodiment). The pusher pins 22are operative to define the chordwise alignment of the spar assembly116/118 in combination with the upper composite skin 110, honeycomb core114 combination as layed-up in the contoured upper airfoil nest 14. Thepusher pins 22 are sized to allow insertion of the pins 22 through thelocator apertures 134 formed in the upper composite skin 110.

Affixed in combination with the support structure 12 at the inboard andoutboard ends of the contoured upper airfoil nest 14 are spar stanchions24. The spar stanchions 24 in operative combination define the spanwisealignment of the spar assembly 116/118 in combination with the uppercomposite skin 110, honeycomb core 114 combination as layed-up in thecontoured upper airfoil nest 14. Also affixed in combination with thesupport structure 16 at each end thereof are a pair of locking members26. One or more hard stops 28 also form part of the support structure 16(see FIG. 3).

The upper assembly 30 comprises a pressure bladder or bag 32, acontoured backplate 34, and a structural support truss 36. The pressurebag 32 is sized to the spanwise and chordwise dimensions of the bladesubassembly 132. For the described embodiment of the growth main rotorblade 100, the pressure bag 32 has dimensions of about 3 feet in thechordwise direction and about 24 feet in the spanwise direction. Thepressure bag 32 is sealingly fastened to the contoured backplate 32, andis pressurized during the compaction process to develop the pressureforces required to compact the blade subassembly 132. The contouredbackplate 34 defines the OML of the lower airfoil surface, i.e., thelower composite skin 112, and is operative to function as a reactionsurface against the back pressures developed in the pressure bag 32during the compaction process.

Due to the overall size of the pressure bag 32, large pressure forcesare developed during pressurization thereof during the compactionprocess (within the range of about 52,000 pounds to about 103,000 poundstotal). The structural support truss 36 is operative to counteract suchlarge pressure forces to prevent damage to the upper assembly 30 duringthe compaction procedure. Each end of the support truss 36 includes apair of complementary locking members 38. When the upper assembly 30 islowered (e.g., by means of a crane) into combination with the lowerassembly 12, the complementary locking members 38 interact with thelocking members 26 to allow the upper and lower assemblies 30, 12 to betemporarily locked in combination, e.g., by pinned connections, toeffectuate the compaction process. A pressure source 40 is pneumaticallyinterconnected with the pressure bag 32 and operative to provide thepressurizing gas to pressurize the pressure bag 32 during the compactionprocess.

As is evident from an examination of FIGS. 2-3, the sheathspreading/insertion apparatus 50 is precisely co-located adjacent thelower assembly 12 of the compaction fixture 10 inasmuch as thecompaction fixture 10 and the sheath spreading/insertion apparatus 50have an interactive functional relationship during the fabricationprotocol of the main rotor blade 100. The sheath spreading/insertionapparatus 50 is operative, during the compaction process effectuated bythe compaction fixture 10, to insert the prefabricated leading edgesheath 120 in combination with the blade subassembly 132 layed-up in thecompaction fixture 10. In the described embodiment, T the sheathspreading/insertion apparatus 50 comprises an elongate stanchion 52having a length corresponding to the span of the leading-edge sheath 120that is movably supported by rolling members 54. The rolling members 54interact with rails 56 secured in combination with an elongate supporttable 58 so that the stanchion 52 is movable with respect to thecompaction fixture 10. The support table 58 is precisely positioned withrespect to the lower assembly 12 to facilitate insertion of the leadingedge sheath 120 in combination with the blade subassembly 132 during thecompaction procedure.

The sheath spreading/insertion apparatus 50 further includes upper firstand lower second elongate carriage members 60U, 60L that are mounted inmovable combination with the elongate stanchion 52. A plurality ofpneumatic cylinders 62U, 62L operatively interconnect the respectivecarriage members 60U, 60L to the stanchion 52. A pressure source 64 ispneumatically interconnected to the pneumatic cylinders 62U, 62L andoperative to provide pressurized air thereto for synchronized movementof the carriage members 60U, 60L with respect to the stanchion 52between a disengaged position, an engaged position, and an operatingposition. While the embodiments of the compaction fixture 10 and thesheath spreading/insertion apparatus 50 described herein utilizeseparate pressure sources 40, 64, it will be appreciated that a commonpressure source may be utilized for the compaction fixture 10 and thesheath spreading/insertion apparatus 50 according to the presentinvention in lieu of the separate pressure sources 40, 64 describedherein.

Pluralities of suction cups 66U, 66L are disposed in alignedcombination, i.e., rows, with the respective carriage members 60U, 60Lalong the spanwise length thereof. For the described embodiment, onehundred and eighty suction cups 66U, 66L are mounted in combination withthe respective carriage members 60U, 60L (ninety suction cups percarriage member). Each individual suction cup 66U, 66L has a bellowedconfiguration (to facilitate engagement of the cups with the contours ofthe respective OML surfaces of the leading-edge sheath 120), and anouter diameter of about two and one-half inches. Each suction cup 66U,66L is capable of exerting a suction force of about 100 to about 175pounds. Suction cups of the type manufactured by PIAB AB, Akersberga,Sweden, may be used in practicing the present invention. The individualsuction cups 66U, 66L are fluidically interconnected to a vacuum source68 which provides suction pressure therefor. The suction cups 66U, 66Lare operative to engage and hold the respective OML surfaces of theleading edge sheath 120 with the vacuum source 68 actuated. Subsequentsynchronized movement of the respective carriage members 60U, 60L awayfrom one another to the operating position causes spreading of thesheath 120 to facilitate insertion thereof in combination with the bladesubassembly 132.

A tip end locator 70 is secured in combination with one end of theelongate stanchion 52 and a plurality of leading edge stops 72 aresecured in combination with the stanchion 52 (see particularly FIG. 3A)along the length thereof. The tip end locator 70 is operative to providespanwise alignment of the leading-edge sheath 120 between the upperfirst and lower second suction cups 66U, 66L to ensure proper insertionthereof in combination with the blade assembly 132. The leading-edgestops 70 are operative to ensure that the leading-edge sheath 120 isproperly inserted between the upper first and lower second suction cups66U, 66L so that the suction cups 66U, 66L can engage and hold the OMLsurfaces of the leading-edge sheath 120.

AIn the described embodiment, a means 74 is provided for moving theelongate stanchion 52 along the rails 56 to insert position theleading-edge sheath 120ontoin relation to the blade subassembly 132 andfor moving the stanchion 52 away from the compaction fixture 10 once theleading-edge sheath 120 is inserted onto positioned in relation to theblade subassembly 132. For the described embodiment, the means 74comprises one or more screw jacks. Mounted on the stanchion 52 are oneor more complementary locator rods 76 that interact with the respectivehard stops 28 of the support structure 16 during movement of thestanchion 52 towards the compaction fixture 10. For the describedembodiment, interaction between the locator rods 76 and the hard stops28 causes a displacement of the locator rods 76. Continued movement ofthe stanchion 52 towards the compaction fixture 10 causes acorresponding displacement of the locator rods 76 until a red bandthereon becomes visible, indicating to the operator of the sheathspreading/insertion positioning apparatus 50 that the leading-edgesheath 120 has been properly inserted onto positioned in relation to theblade subassembly 132. One skilled in the art will appreciate that othermeans may be utilized to indicate that movement of the stanchion 52should be terminated inasmuch as the leading-edge sheath 120 has beenproperly inserted onto the blade subassembly 132. For example, thelocator rods 76 and the respective hard stops 28 could be functionallyconfigured and positioned so that contact therebetween automaticallyterminates the operation of the moving means 74 such that the stanchion52 ceases moving.

The steps of an assemblage and compaction process 200 according to thepresent invention are schematically illustrated in FIG. 4A. The purposeof the assemblage and compaction process according to the presentinvention is to assemble the components of the main rotor blade 100described hereinabove into a cure configuration. The cure configurationof the main rotor blade 100 is inserted into an autoclave (not shown)for final cure to form the finished main rotor blade assembly 100exemplarily illustrated in FIG. 1A. The upper composite skin 110 and thehoneycomb core 114 are provided as a prefabricated combination 110/114for the initial step 202 of the described embodiment of the assemblageand compaction protocol. This is achieved by applying a suitable filmadhesive to the honeycomb core 114 which is then mounted on the uppercomposite skin 110 and the combination 110/114 is then cured. In step202, the prefabricated combination 110/114 is layed-up in the contouredupper airfoil nest 14 by aligning the trailing edge 104 of the uppercomposite skin 110 with the tooling pins 20 and inserting the locatorapertures 134 of the upper composite skin 110 onto the pusher pins 22.While providing the upper composite skin 110 and the honeycomb core 114as a prefabricated combination 110/114 simplifies the assemblage andcompaction process according to the present invention, one skilled inthe art will appreciate that the upper composite skin 110 and thehoneycomb core 114 may alternatively be individually layed-up incombination with the contoured upper airfoil nest 14 in separatesequential steps.

A suitable film adhesive is then applied in step 204 prior to lay-up ofthe spar assembly 116/118. The film adhesive may be applied directly tothe spar assembly 116/118, or alternatively, directly to the layed-upupper composite skin 110. The spar assembly 116/118 is then layed-up incombination with the layed-up upper composite skin, honeycomb corecombination 110/114 in step 206. Proper chordwise alignment of the sparassembly 116/118 is achieved by abutting the spar assembly 116/118against the pusher pins 22 protruding through the upper composite skin102. Proper spanwise alignment of the spar assembly 116/118 is achievedby ensuring that the ends of the spar assembly 116/118 abut the sparstanchions 24. A suitable adhesive is applied to the exposed surfaces ofthe honeycomb core 114 and the spar assembly 116/118 in step 208, andthen the lower composite skin 112 is layed-up on adhesive-coatedhoneycomb core 114 and spar assembly 116/118 in step 210. The assembledcombination of the upper composite skin 110 and honeycomb core 114combination, the spar assembly 116/118, and the lower composite skin 112define the blade subassembly 132 components assembled in the lowerassembly 12 of the compaction fixture 10.

Prior to lowering and locking the upper assembly 30 in combination withthe lower assembly 12, a caul plate 42 is preferably inserted betweenthe spar subassembly 132 and the upper assembly 30 in step 212. The caulplate 42 is formed from a plurality of composite plies, e.g. for thedescribed embodiment five to nine prepreg fiberglass plies. The caulplate 42 is configured to conform to the lower composite skin 112 of theblade subassembly 132 and is operative to provide an even pressuredistribution over the blade subassembly 132 components during compactionthereof. After insertion of the caul plate 42 in optional step 212, theupper assembly 30 is lowered and locked in combination with the lowerassembly 12 by means of pinned connections between the respectivelocking members 26, 38 in step 214. Close-out blocks (not illustrated)preferably have been inserted at the inboard and outboard ends 106, 108of the blade subassembly 132 prior to locking the upper and lowerassemblies 12, 30 in combination. The close-out blocks are operative toprevent blade tip and root end round out during compaction of the bladesubassembly 132.

With the upper assembly 30 locked in combination with the lower assembly12, the leading-edge segment (see reference numeral 138 in FIG. 3) ofthe assembled blade subassembly 132 protrudes outwardly from thecompaction fixture 10, i.e., is not enclosed by the compaction fixture10. The pressure source 40 is actuated to pressurize the pressure bag 32in step 216, which exerts pressure forces via the caul plate 42 (ordirectly if the caul plate 42 is not utilized) to compact the assembledblade subassembly 132. For the described embodiment, the pressure bag 32is pressurized so that pressure forces within the range of about 5 psito about 10 psi are exerted against the assembled blade subassembly 132.The assembled blade subassembly 132 is subjected to compaction pressurefor a predetermined compaction period in step 218. For the describedembodiment of the main rotor blade 100, the described assemblage andcompaction process has a compaction period within the range of about tenminutes to about fifteen minutes.

During the compaction period the leading-edge sheath 120 is spread andinserted onto positioned in relation to the exposed leading-edge segment138 of the assembled blade subassembly 132 by means of a sheathspreading and insertion positioning process 300 according to the presentinvention as illustrated in FIG. 4B. Prior to insertion positioning ofthe leading-edge sheath 120, a suitable adhesive is applied to theexposed leading-edge segment 138 in step P1 (alternatively the adhesivemay be applied to the IML surfaces of the prepreg composite plies 122 ofthe leading-edge sheath 120).

With the upper first and lower second carriage members 60U, 60L in adisengaged position, the leading-edge sheath 120 is inserted between theupper first and lower second suction cups 66U, 66L in step 302. Thedisengaged position of the carriage members 60U, 60L facilitates suchinsertion without any physical contact between the leading-edge sheath120 and the suction cups 66U, 66L. Proper insertion of the leading-edgesheath 120 is ensured by the abutting engagement of the sheath 120against the tip end locator 70 and the leading edge stops 72. Thepressure source 64 is actuated to allow synchronized movement of thecarriage members 60U, 60L to an engaged position in step 304 wherein thesuction cups 66U, 66L abuttingly engage the leading-edge sheath 120.

The vacuum source 68 is then actuated, causing the suction cups 66U, 66Lto exert suction forces against the respective OML surfaces of theleading-edge sheath 120 in step 306. The suction forces exerted by thesuction cups 66U, 66L are of sufficient strength that the leading-edgesheath 120 remains in engaged combination, i.e., held, by the suctioncups 66U, 66L. The pressure source 64 is actuated to allow synchronizedmovement of the carriage members 60U, 60L back towards the open positionto the operating position. Since the suction cups 66U, 66L are exertingsuction forces to hold the leading-edge sheath 120, the synchronizedmovement of the carriage members 60U, 60L to the operating positioncauses the exposed segments 128 of the sheath 120 to spread apart. Forthe described embodiment, the finished edges 128A (see FIG. 1C) of theexposed segments 128 of the sheath 120 are typically spaced apart byabout one and one-half inches in the normal spaced-apart state. Due tothe action of the sheath spreading/insertion apparatus 50, the finishededges 128A of the exposed segments 128 of the sheath 120 are spreadapart to a spread-apart condition defined by a separation distance ofabout two and one-half to three inches between the opposed segments 128when the carriage members 60U, 60L are moved to the operating position.The spread-apart configuration of the leading-edge sheath 120facilitates insertion positioning thereof onto in relation to theexposed segment 138 of the blade subassembly 132.

ToIn the described embodiment, to insert the spread-apart leading-edgesheath 120, the stanchion moving means 74 is actuated to move thestanchion 52 towards the compaction fixture 10 for insertion positioningof the spread-apart leading-edge sheath 120 in step 310. Properinsertion positioning of the leading-edge sheath 120 is indicated by thevisibility of the red band of the locator rods 76. With the leading-edgesheath 120 fully inserted onto positioned in relation to the exposedsegment 138 of the blade subassembly 132, the hardpoints 136 of thecounterweights 118 abuttingly engage the IML of the leading-edge sheath120, the exposed segments 128 of the prepreg composite plies 122underlie the upper and lower composite skins 110, 112, and the edges ofthe upper and lower composite skins 110, 112 abuttingly engage therespective edges of the titanium strips 124.

Once the leading-edge sheath 120 is fully inserted onto positioned inrelation to the exposed segment 138 of the blade subassembly 132, thepressure source 64 is actuated to cause synchronized movement of theupper first and lower second carriage members 60U, 60L to the engagedposition in step 312. Such synchronized movement allows the spread-partleading-edge sheath 120 to return to its normal spread-apart state,i.e., for the described embodiment, from a spread-apart condition ofabout two and one-half to three inches to about one and one-half inches.In the normal spaced-apart state, the leading-edge sheath 120 exerts acompaction force against the blade subassembly 132 to facilitateadhesive bonding of the leading-edge sheath 120 in combination with theblade subassembly 132. The vacuum source 68 is shut down in step 314,which terminates the suction forces exerted by the upper first and lowersecond suction cups 66U, 66L against the leading-edge sheath 120. Thepressure source is actuated to cause synchronized movement of thecarriage members 60U, 60L back to the disengaged position in step 316.Finally, in step 318 the stanchion 52 is returned to the startingposition wherein the spreading and insertion positioning process may berepeated as required.

Once the compaction period has elapsed, the locking members 26, 38 areunlocked, and a crane is utilized to remove the upper assembly 30 fromthe lower assembly 12 in step 222. The assembled main rotor blade 100 isthen removed from the contoured upper airfoil nest 14. The assembledmain rotor blade 100 is subsequently cured in an autoclave to form afinished main rotor blade assembly 100.

A variety of modifications and variations of the above-describedapparatus and methods for fabricating a main rotor blade are possible inlight of the above teachings. It is therefore to be understood that,within the scope of the appended claims, the present invention may bepracticed otherwise than as specifically described hereinabove.

What is claimed is:
 1. A method for assembling and compacting a bladesubassembly that includes an upper composite skin, a lower compositeskin, a honeycomb core, and a spar assembly, comprising the steps of:providing a composite fixture that includes a lower assembly having acontoured upper airfoil nest mounted on a support structure and an upperassembly having a structural support truss, a contoured backplateaffixed to the structural support truss, and a pressure bag fastened insealed combination with the contoured backplate; laying up the uppercomposite skin and the honeycomb core in combination in the contouredupper airfoil nest; locating the spar assembly in chordwise and spanwisealignment in the contoured upper airfoil nest; laying up said lowercomposite skin in combination with the spar assembly and the honeycombcore; locking the upper assembly and the lower assembly in combination;and pressurizing the pressure bag to compact the blade subassembly. 2.The method of claim 1 further comprising the step of inserting a caulplate between the upper assembly and the lower assembly prior to saidlocking step.
 3. A method for spreading and inserting positioning aleading-edge sheath onto in relation to a blade subassembly, comprisingthe steps of: mounting the leading-edge sheath between upper first andlower second rows of suction cups; imparting synchronized movement tothe upper first and lower second rows of suction cups to an engagedposition wherein the suction cups are in abutting engagement withrespective OML surfaces of the leading edge sheath; generating suctionforces in the upper first and lower second rows of suction cups to causethe suction cups to hold the respective OML surfaces of the leading-edgesheath; imparting synchronized movement to the upper first and lowersecond rows of suction cups to an operating position to cause theleading-edge sheath to be spread apart; and insertingpositioning thespread-apart leading-edge sheath ontoin relation to the bladesubassembly.